We can't use up_panel and down_panel as differentiators for the buttons, because these window system resources don't exist before realize(). Just use a one-off enum for this purpose.
https://bugzilla.gnome.org/show_bug.cgi?id=758094
cf7bb4f spin button: Fix initial button state
gtk/gtkspinbutton.c | 33 +++++++++++++++++++--------------
1 file changed, 19 insertions(+), 14 deletions(-)
Upstream: git.gnome.org